This disclosure relates to a data storage media, and especially relates to a colored data storage media.
Digital Versatile Disks (or DVDs) are slowly but surely taking over compact disks (CDs). These formats provide significantly more storage capacity than CDs thus allowing the recording of up to 8 hours of video/audio content with high digital quality. The number of DVDs sold on the market will likely exceed 1 billion units globally in 2001 and is expected to reach about 4 billion by 2004.
To achieve the high storage density in a disk that has the same overall dimensions as a CD, the disk construction has been changed. The most fundamental and visible difference is that a DVD is no longer made of a single 1.2 mm thick plastic substrate but of two 0.6 mm halves that are bonded together (“DVD Demystified:” by Jim Taylor, ed. McGraw Hill, 1998). In addition, the reading laser wavelength has changed from 780 nanometers (nm) in CDs, which is located in the near infrared part of the spectrum, to 635 or 650 nm for DVDs that is located in the visible spectrum. Depending on the type of DVD (DVD-5, DVD-9, DVD-10, DVD-14, DVD-18, DVD-R, DVD-RW, etc.), the construction can vary substantially, going from a single side/single layer (DVD-5) to double side/double layer (DVD-18), not to mention the recordable formats such as DVD-R and DVD-RW. The tight specifications (European Association for Standardizing Information and Communication Systems (“ECMA”) Specifications #267 for 1.20 mm DVD-Read only disk) imposed by the Optical Media consortium, combined with the fact that the laser wavelength is located in the visible spectrum makes DVD manufacturing a challenge.
The optical properties of the substrate are not the only requirements for DVDs. For example, the size of the pits is much smaller in a DVD, which implies that a DVD is more sensitive to resin quality (impurities) than a CD. Due to their thinner gage (0.6 mm instead of 1.2 mm), DVDs are also more challenging than CDs in terms of molding. In fact, the rheology (flow characteristics) of the resin is important and tightly controlled. Additionally, inconsistencies in the thickness of the disk body are also a source of defects in optical disks. A DVD is much more sensitive to the presence of such defects because it is not only thinner and read in the visible spectrum, but it is also read at a higher rotational/scanning speed than a regular CD. The most advanced DVD formats that are multi-layered (as for example DVD-9, DVD-14 and DVD-18) represent the highest degree o both a fully reflective and a semi-reflective layer associated with 2 layers of pits (e.g., patterning which forms geographic locators). Single layered DVDs, i.e. DVD-5 and DVD-10, do not have the semi-reflective layer and contain only one layer of pits. As a result of the differences in the disk construction, reflectivity requirements are very different between single layered and multi-layered disks.
To date, all the pre-recorded or recordable multi-layered DVDs available on the market are made with colorless resin. The only aesthetic difference between DVDs comes from the metallization (i.e., the data layer). For example a gold disk is obtained when gold is used, and similarly, a bright silver look is obtained with silver, silver alloy or aluminum.